Insects are becoming smaller: miniaturization

According to different studies, multicellular organisms tend to become smaller and smaller through time. This phenomenon is called miniaturization and is considered one of the most significative evolutionary trends among insects. Miniaturization is a driving force for diversity and evolutionary novelties, even though it must deal with some limitations.

Learn more about this phenomenon and met some of the most extreme cases of miniaturization among insects through this post.

Why are animals becoming smaller?

For some years now, multiple studies suggest there is a widely extended trend to miniaturization among multicellular animals (i. e. organisms composed by more than one cell).

Miniaturization is a remarkable natural phenomenon headed to the evolution of extremely small bodies. This process has been observed in different non-related groups of animals:

• Shrews (Soricomorpha: Soricidae), mammals.
• Hummingbirds (Apodiformes: Trochilidae), birds.
• Diverse groups of insects and arachnids.

To know more about giant insects, you can read “Size matters (for insects)!“

Diversification and speciation processes have given place to lots of new species through time, all of them constantly competing for limited space and food sources. This scenario turns even more drastic in tropical regions, where diversification rates are extremely high.

Learn about the ecological niche concept by reading “The living space of organisms“.

Facing the increasing demands of space and resources, evolution has given place to numerous curious phenomena such as miniaturization to solve these problems: by becoming smaller, organisms (either free-living or parasites) gain access to new ecological niches, get new food sources and avoid predation.

Despite many animals tend to miniaturization, this phenomenon is more frequently observed among arthropods, being one of their most remarkable evolutionary trends. Moreover, arthropods hold the record of the smallest multicellular organisms known to date, some of which are even smaller than an amoeba!

Guinness World Record of the smallest insects

The smallest arthropods are crustaceans belonging to the subclass Tantulocarida, which are ectoparasites of other groups of crustaceans, such as copepods or amphipodes. The species Tantulacus dieteri is still considered the smallest species of arthropods worldwide, which barely measures 85 micrometers (0,085 millimeters), thus being smaller than many unicellular life beings.

However, insects do not lag far behind.

Mymaridae

Mymaridae (or fairyflies) are a family of wasps inside the superfamily Chalcidoidea from temperate and tropical regions. Adults, ranging from 0.5 to 1 millimeter, develop as parasites of other insects’ eggs (e. g. bugs, Heteroptera). For this reason, fairyflies are very valuable as biological control agents of some harmful pests. Also, they are amongst the smallest insects worldwide.

Currently, the one holding the record as the smallest known adult insect is the apterous (wingless) male of the species Dicopomorpha echmepterygis from Costa Rica, with a registered minimum size of 0.139 millimeters. They neither have eyes nor mouthparts, and their legs endings are deeply modified to get attached to the females (somewhat bigger and winged) time enough to fertilize them. They are even smaller than a paramecium, a unicellular organism!

You can read “Basic microbiology (I): invisible world” to know more about unicellular organisms.

Male of D. echmepterygis. Link.

Fairyflies also include the smallest winged insects worldwide: the species Kikiki huna from Hawaii, with and approximate size of 0.15 millimeters.

Trichogrammatidae

Like fairyflies, trichogrammatids are tiny wasps of the superfamily Chalcidoidea that parasite eggs of other insects, especially lepidopterans (butterflies and moths). Adults of almost all the species measure less than 1 millimeter and are distributed worldwide. Adult males of some species are wingless and mate with their own sisters within the host egg, dying shortly after without even leaving it.

The genus Megaphragma contains two of the smallest insects worldwide after fairyflies: Megaphragma caribea (0.17 millimeters) and Megaphragma mymaripenne (0.2 millimeters), from Hawaii.

A) M. mymaripenne; B) Paramecium caudatum. Link.

Trichogrammatids also have one of the smallest known nervous systems, and that of the species M. mymaripenne is one of the most reduced and specials worldwide, as it is composed by only 7400 neurons without nucleus. During the pupae stage, this insect develops neurons with functional nuclei which are able to synthetize enough proteins for the entire adulthood. Once adulthood is reached, neurons lose their nuclei and become smaller, thus saving space.

Ptiliidae

Ptiliidae is a cosmopolitan family of tiny beetles known for including the smallest non-parasitic insects worldwide: the genera Nanosella and Scydosella.

Ptiliidae eggs are very large in comparison with the adult female size, so they can develop a single egg at a time. Other species undergo parthenogenesis.

Learn some more about parthenogensis by reading “Immaculate Conception…in reptiles and insects“.

Currently, the smallest Ptiliidae species known and so the smallest non-parasitic (free living) insect worldwide is Scydosella musawasensis (0.3 millimeters), from Nicaragua and Colombia.

Scydosella musawasensis. Link (original picture: Polilov, A (2015) How small is the smallest? New record and remeasuring of Scydosella musawasensis Hall, 1999 (Coleoptera, Ptiliidae), the smallest known free-living insect).

Consequences of miniaturization

Miniaturization gives rise to many anatomical and physiological changes, generally aimed at the simplification of structures. According to Gorodkov (1984), the limit size of miniaturization is 1 millimeter; under this critical value, the body would suffer from deep simplifications that would hinder multicellular life.

While this simplification process takes places within some groups of invertebrates, insects have demonstrated that they can overcome this limit without too many signs of simplification (conserving a large number of cells and having a greater anatomical complexity than other organisms with a similar size) and also giving rise to evolutionary novelties (e. g. neurons without nucleus as M. mymaripenne).

However, getting so small usually entails some consequences:

• Simplification or loss of certain physiological functions: loss of wings (and, consequently, flight capacity), legs (or extreme modifications), mouthparts, sensory organs.
• Considerable changes in the effects associated with certain physical forces or environmental parameters: capillary forces, air viscosity or diffusion rate, all of them associated with the extreme reduction of circulatory and tracheal (or respiratory) systems. That is, being smaller alters the internal movements of gases and liquids.

So, does miniaturization have a limit?

The answer is yes, although insects seem to resist to it.

There are several hypotheses about the organ that limits miniaturization. Both the nervous and the reproductive systems, as well as the sensory organs, are very intolerant to miniaturization: they must be large enough to be functional, since their functions would be endangered by a limited size; and so, the multicellular life.

.             .            .

Multicellular life reduction seems to have no limits. Will we find an even smaller insect? Time will tell.

Main picture: link.

Lying birds: Brood parasitism in birds, the continual struggle for survival

Some birds have development an interesting reproductive strategy to deceive other birds and put the eggs in their nests, so foster parents are forced to feed other chicks. But what is behind this strange behaviour?

WHAT IS THE BROOD PARASITISM AND HOW MANY DIFFERENT TYPES ARE THERE?

The brood parasitism is a type of biological interaction between two organisms, in which one of them (the parasite) obtains resources from the other one (the host). In birds, the parasite obtains some benefits of parental cares from the host, developing a breeding strategy cold brood parasitism. The brood parasitism, although has been studied mostly in birds, also happens in other groups of vertebrates: for example in fish (Sato 1986, Baba et al. 1990) and some insects such as Himenoptera, Coleoptera and Heteropterous.

Brood parasitism – server.ege.fcen.uba.ar

According the characteristics of each relation, there are different types of brood parasitism:

• Optional brood parasitism: the parasite species is capable of breeding a part of its own offspring and also, to parasite other individuals. A example in birds is in genus Coccyzus (Cuculidae).
• Forced brood parasitism: hosts breed all the offspring of the parasite bird, as happens in common cucko (Cuculus canorus).
• Intraspecific brood parasitism: host and parasite are of the same species. This is a common strategy in colonial species and in other species with nidifugous chicks.
• Interspecific brood parasitism: host and parasite are the different species.

In addition parasites are classified, by their specialisation on one or several host species, in general parasites (parasite large number of species) or specialist (only parasite one or a few species).

WHAT IS THE ORIGIN OF THIS BEHAVIOUR?

Everything suggests that the main focus of this behavior was decreased the parental investment (less cost) increasing the chance of success (major benefits), although this is not always the case.

There are several hyphotesis to explain the origin of the brood parasitism in birds:

1. Firstly, it is probably that parasites were displaced individuals that did not have any territory or lost their laying, and they try to lay their eggs in other nests to achieve greater breeding success (Sorenson 1998, Sandell y Diemer 1999).
2. Other hypothesis suggests that this parasitism could be a stable strategy for evolution of the population, which has similar benefits to breed its own offspring (Eadie y Fryxell 1992).
3. Finally, the third hyphotesis considers this parasitism like an additional strategy to the parent care and some individuals could be used it to reduce the sibling competition in their nest, or to reduce the number of chicks to feed without decreasing the breeding success (Moller 1987, Jackson 1993).

 

HOW CAN THEY PROTECT THEMSELVES?

Hosts have learned to protect their offspring about the threat posed by brood parasitism.

Common cuckoo (Cuculus canorus) and rufous bush robin (Cercotrichas galactotes) have this relation, the first one lay a egg in the rufuos bush robin nest that it will be born before other chicks and kill them, capturing all the parental care.

One of the main host defences against brood parasites is the recognition and rejection of parasitic eggs. Because obligated brood parasites need appropriated individuals hosts for reproduction, such host defence-mechanisms simultaneously select for counter-defences in brood parasites, causing a coevolutionary arms race between hosts and parasites.

Rejection of parasitic eggs – server.ege.fcen.uba.ar

 

A FIGHT CONSTANTLY EVOLVING

There is a particular case, the strategy of the great spotted cuckoo (Clamator glandarius) when is a parasite of the common magpie (Pica pica). The great spotted cuckoo lays an egg in the nest of common magpie and this chick possess adaptations to exploit the host parental care, it does not kill directly their siblings but has advantages in relation to begging behaviour and in the order of birth (cuckoo chick is born four or six days before magpie chicks.

Common magpie (Pica pica) – http://waste.ideal.es

Magpies have development a selective advantage to recognize and ejection of parasitic egg. However, it has been observed that cuckoos react to this behaviour returning to the parasitized nest and destroying it. This situation conditions the behaviour of the magpies in the future and they are forced to accept the parasite egg.

Eggs of cuckoo in magpie nest – http://eldiariodelasaves.wordpress.com

Cuckoo chicks are born some days before magpie chicks – http://eldiariodelasaves.wordpress.com

Development of cuckoo chicks in the nest – http://eldiariodelasaves.wordpress.com

The result of this evolutionary fight is the mafia-type behaviour of cuckoo that leads to a co-evolutionary arms race between species to avoid parasitism, in one hand, and maintain it, in the other one.

Great Spotted Cuckoo (Clamator glandarius) – Fveronesi1. Flickr, Creative Commons

REFERENCES

• Parasitism and nest predation in parasitic cuckoo (American Naturalist, 1995)
• Mafia Behaviour and the Evolution of Facultative Virulence (Journal of Theoretical Biology, 1995.)
• Magpie Host Manipulation by Great Spotted Cuckoos: Evidence for an Avian Mafia? (Evolution, 1997.)

• Retaliatory mafia behavior by a parasitic cowbird favors host acceptance of parasitic eggs (PNAS, 2006)

• Cover photo: Cuckoo chick in parasitic nest reciving food of host – http://www.guaso.com/bestiario_el_cuco.htm

 

 

Parasites: signs on our way

The mysteries of human evolution, their development and their movementsthroughout history continue to create great interest and expectation. There are stillmany things to discover and understand about ancient societies, but thanks to thehelp of the science we are increasingly closer. Can parasites of the past shed light on those communities? We will discover it in thehands of the paleoparasitology.

WHAT IS PALEOPARASITOLOGY?

This is a branch of paleontology that study parasitological evidences in archaeological records, i.e.,studying parasites or remains of these found in ancient archaeological sites. The objective of these studies is to shed light on the origin and evolution of parasitic diseases that exist, as well as determine their phylogenetic relationships.  The study of ancient parasites allows us to know socio-cultural aspects of ancient societies as for example their diets, their level of hygiene, if human  were nomadic or sedentary, their migrations etc.

The materials studied by the paleoparasitology are generally fossilized tissueremains, mummies, fossils, coprolites (feces mummified) or sediments that have been able to be in contact with those who were the hosts of these parasites.

Mummified human coprolites. (Image: M. Beltrame)

Find remains of a parasite in some of the samples is difficult, since the passage oftime destroys all evidence. Even so, usually eggs or Oocyst parasites found (since theyare forms of resistance that have managed to stay over the millennia).

A egg of a louse (Pediculus humanus) found in a mummy of Brazil (12,000 years old). B. egg of Trichuris sp. found in Cape virgins, Argentina (6000 years old). (Image: Araujo).

In certain cases, manuscripts and drawings of ancient societies have providedinformation on the presence of certain parasites, such as for example ceramics thatwe observe below, where lesions that presents a person who suffers from cutaneous leishmaniasis is faithfully represented. In the next image we see a fossilized skull which presents very similar lesions.

A. Modified image of a ceramic moche representing (red circle) lesions caused by leishmaniasis. (Image: Oscar Anton, Pinterest) B. mummified skull that shows very similar injuries. (Image: Karl J. Reinhard).

THE ARRIVAL TO AMERICA: HUMAN MIGRATIONS AND PARASITES

About 150,000 years ago appeared a new species of hominid in Africa: Homo sapiens. It began to expand in several waves to the rest of the continent, Europe, and Asia,carrying with them some parasites that had inherited from his ancestors (known as heirloom parasites). At the same time, they were acquiring along their journey a range of parasites due to interactions with other humans and animals (souvenir parasites).

Following the archaeological remains and parasitological  clues what ancient humans have left during their migrations, is possible to determine the routes followed by them. One of these routes was the arrival in the new world (America). We have always believed that the first inhabitants of the Americas came across the Beringia Strait (which joined at some point by ice Siberia with Alaska) about 13,000 years ago.

Representation of the path followed by the first American settlers by the Beringia Strait Bridge. (Image: The siberian Times).

A few very interesting parasites that can be found in the American archaeological remains are Trichuris trichiura (nematode known as whipworm  and Ancylostoma duodenale (hookworm). These parasites need tropical or subtropical climatic conditions since the eggs are expelled with faeces and mature in the ground.

A. At the top adult A. duodenale (Christopher Noble). At bottom we can view an A.duodenale egg (Image: Universidad Antioquia) B. Adult Trichuris trichiura (Invertebrate zoology Virtual collection) and at bottom its egg. (Microbiolgia blogspot).

How do they then survived the cold conditions of the regions of Siberia and Alaska in the last ice age? They could not. These parasites would have not survived those harsh climatic conditions, since to their maturation and transformation infective they need warm and moist environments. In addition, signs of infections not found by these parasites in Arctic populations, such as the Inuit.

So, researchers believe that migration across the Bering Strait was not the only one. Paleoparasitologic experts  Adauto Aráujo and Karl J. Reinhard proposed that there were two alternative routes. On the one hand proposed a costal route (along the coast, route b in the image) and a trans-pacific route (crossing the Pacific Ocean, route c). By these routes parasites had been able to survive and continue infecting humans.

The arrival of man in America routes proposed by Aráujo and Reinhard based on paleoparasitologic remains. (Image: Aráujo, et al.)

Could they have been already there? This question has an easy answer. These intestinal parasites are specific from man, therefore, they need human hosts to complete their life cycles. If there were no humans in America, surely there would be this kind of parasites.

Another  parasitological fact that confirm this theory is the presence of Enterobius vermicularis, popularly known as pinworm. This parasite was linked for the first time to the ancestors of Homo sapiens and throughout history, has coevolved with them to give rise to several different subspecies. On the American continent have been found remains of two lineages of E.vermicularis, that could be because arrived hominids from different places with different parasites. In this case, the parasite if he could get through the Beringia Strait, since its life cycle does not depend so strongly on the environmental conditions.

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“Parasites suffer the same phenomena for evolution that humans and other organisms, as selection, extinction and colonization. For this reason, these specific parasites of man are excellent evidence that shed light on the movements of our ancestors”Adauto Aráujo, 2008.

REFERENCES

• A, Aráujo (2008). Parasites as Probes for Prehistoric Human Migrations?. Trends In Parasitology. Vol 24 (3). Pages: 112-115.
• Karl, J. Reinhard (2008). Archaeoparasitology. Encyclopedia of Archaeology, p. 494-501, ed. por Deborah M. Pearsall.
• CDC. Laboratory Identification of Parasitic Diseases of Public Health Concern. (En inglés).
• Cover photo: Chris Stringer, Natural History  Museum (Londres)

The killer fungus: the nightmare of the amphibians

In recent years, the populations of amphibians around the world have suffered a major decline, to the point that many of them disappear completely. Many researchers are running that the loss of these populations is due to several factors: climate change, habitat loss and the presence of a parasitic fungus. In this article will announce the parasite known as killer fungus.

BATRACHOCYTRIUM DENDROBATIDIS 

This is the scientific name given to this fungus. It belongs to the class Chytridiomycetes, which gathers fungus parasites of plants and invertebrates. However, this is the only one of this kind affecting vertebrate organisms. It is related to the disappearance of more than 200 species of amphibians, including the golden toad of Costa Rica.

One of the latest images that we have of the golden toad (Almirante periglenes). (Photo: Richard K.)

It has a life cycle that consists of two phases: a stationary (sporangium) and one mobile (via zoospores). In the image below we can see an outline of the structure of this type of fungi. The sporangium has some fine extensions known as rhizoids or mycelium rizoidal that allows to anchor itself in the inner skin layer. The zoospore emerges from the sporangium when it matures and presents a single apical flagellum.

Diagram of the structure of the fungus Bd. (photo: trilobite glassworks)

Batrachocytrium dedrobatidis is a parasite and need a host that provide nutrients. In this case, the fungus feeds on keratin of skin of amphibians. Zoospores arrives to the skin of the host by water and encyst in the areas with greatest amount of keratin. They lose the flagel and become a sporangium. They develop the mycelium and again produce zoospores that emerge into the water. In the event that there are no hosts around, the parasite becomes a saprophyte (feeds on organic matter in decomposition) waiting for the arrival of new amphibians.

Life cycle of B. dendrobatidis. (Photo: Roseblum)

Why this process results in a disease for amphibians?

CHYTRIDIOMYCOSIS

In amphibians, the skin is one of the most important organs. It develops functions such as hydration, osmoregulation, the thermoregulation and breathing (for example, the lissamphibians breathe only through the skin. Discover them in this article). Fungus feeds on keratin of skin, destroys the upper layers and spread over all body surface, preventing this organ to perform ion exchange. Individuals die from cardiac arrest.

Image of microscopy of skin of an amphibian stricken with chytridiomycosis. The arrows indicate the sporangia. (Photo: Che Weldon)

The sporangia are attached to keratinized skin areas, which get their nutrients. Approximately between 4 and 6 days after infection, they begin to develop the zoospores (black areas in the interior of the sporangia of the image above).When these spores have matured, are released through a spout that is initially closed. Stopper (bottom image) dissolves shortly before the release of zoospores.

Image of the surface of the skin of a frog by electronic scanner. The papillae of the sporangium are identified with a triangle. The black arrow indicates a sporangium with the plug dissolved. (Photo: Berger).

This disease affects only adult specimens. Even so, tadpoles are reservoirs of the disease, so they can become infected but do not develop symptoms. The fungus infects the tadpole keratinized areas (normally the areas of the mouth) and when the metamorphosis takes place, the fungus expands to other areas.

GEOGRAPHIC EXPANSION: ARRIVAL TO SPAIN

The fungus is characteristic of South African populations of Xenopus laevis (African Toad of nails, used in research), but spread all over the world through the traffic from infected individuals. The situation is so serious and the world Organization for Animal Health (OiE) has classified chytridiomycosis as a notifiable disease. In addition B. dendrobatidis is included in the list of 100 most invasive exotic species by the IUCN (if you want to know that they are invasive species, please read the following article).

World regions which have been confirmed positive cases of chytridiomycosis. (Photo: Bd-maps).

Spain was the first European country to suffer an outbreak of chytridiomycosis, particularly in the Parque Natural de Peñalara in Madrid. The common midwife toad (Alytes obstetricans) was the most affected. Positive cases in other Spanish regions, as for example in the Balearic Islands have also been found. There are many investigations underway to solve this problem, like for example of Project Zero of the CSIC General Foundation.

Positive amphibians to chytridiomycosis in Spain (photo: Bd-maps)

THE CASE OF THE BALEARIC MIDWIFE TOAD

The Balearic midwife Toad  (Alytes muletensis) is endemic to the Balearic Islands. It is classified as a vulnerable species by the IUCN (in this article we talk about this organization and its red list of species). It lives in ponds and ravines of difficult access in the Serra de Tramuntana (Mallorca). Specimens can reach around 4 cm and are nocturnal. Generally, this species was threatened by the destruction of their habitat or predation, but the latest threat facing it is chytridiomycosis.

Balearic midwife Toad or ferreret (photo: Guillem Gutiérrez).

Researchers found that certain populations experienced a significant decrease in the number of specimens, and they appeared dead without apparent reason. Studies revealed that these deaths were due to the presence of the parasitic fungus B.dendrobatidis. The population that presented more problems was the belonging to the area known as Torrent dels Ferrets (in 2004 it was confirmed the first case of chytridiomycosis).

Evolution of the population of Alytes muletensis in the Torrent dels Ferrerets. There have been deaths by Bd since 2004 (photo: Joan Mayol)

Research to ending this fungus has been a success. At the end of 2015, researchers from the Balearic Islands confirmed the first successful treatment against chytridiomycosis. They carried out disinfection in the natural environment (to eliminate any presence of zoospore) and combined it with an anti-fungal treatment to tadpoles. They managed to completely eliminate the presence of the parasite, and thus save the population. Even so, efforts to put an end to this fungus should not cease.

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Chytridiomycosis is still a serious problem for global amphibian populations, but there is still hope. 

REFERENCES

• World organisation for animal health (OiE)
• CSIC General Foundation: Lucha sin cuartel contra la quitridiomicosis (spanish), by Jaume Bosch.
• 100 of the most invasive alien species in the world, ISSG. PDF
• The Mallorcan midwife Toad, from discovery to conservation, Joan Mayol and Joan Oliver. (Spanish)
• Cover Photo: Vance Vredenburg.

 

Evolution for beginners 2: coevolution

After the success of Evolution for beginners, today we’ll continue  knowing the basics of biological evolution. Why  exist insects that seem orchids and vice versa? Why gazelles and cheetahs are almost equally fast? Why your dog understands you? In other words, what is coevolution?

WHAT IS COEVOLUTION?

We know that it is inevitable that living beings establish symbiotic relationships between them. Some depend on others to survive, and at the same time, on elements of their environtment as water, light or air. These mutual pressures between species make that evolve together, and as one evolve as a species, in turn it forces the other to evolve. Let’s see some examples:

POLLINATION

The most known process of coevolution is pollination. It was actually the first co-evolutionary study (1859) by Darwin, although he didn’t use that term. The first to use the word coevolution were Ehrlich and Raven (1964).

Insects existed long before the appearance of flowering plants, but their success was due to the discovery that nectar is a good reserve of energy. In turn, the plants found in the insects another way more effectively to carry pollen to another flower. Pollination by the wind (anemophily) requires more production of pollen and a good dose of luck to at least fertilize some flowers of the same species. Many plants have developed flowers that trap insects until they are covered with pollen and then set them free. These insects have hairs in their body to enable this process. In turn some animals have developed long appendages (beaks of hummingbirds, butterflies’ proboscis…) to access the nectar.

Darwin’s moth (Xantophan morganii praedicta). Photo by Minden Pictures/Superstock

It is the famous case of the Darwin’s moth (Xanthopan morganii praedicta) of which we have already talked about. Charles Darwin, studying orchid Christmas (Angraecum sesquipedale) saw that the nectar was 29 cm inside the flower. He sensed that there should exist an animal with a proboscis of this size. Eleven years later, Alfred Russell Wallace reported him that the Morgan’s sphinxs had proboscis over 20 cm long, and a time later they were found in the same area where Darwin had studied that species of orchid (Madagascar). In honor of both it was added “praedicta” to the scientific name.

There are also bee orchids that mimic female insects to ensure their pollination. To learn more about these orchids and the Christmas one, do not miss this post by Adriel.

The bat Anoura fistulata and its long tongue. Photo by Nathan Muchhala

But many plants not only depend on insects, also some birds (like humming birds) and mammals (such as bats) are essential to pollination. The record for the longest mammal tongue in the world is for a bat from Ecuador (Anoura fistulata); its tongue measures 8 cm (150% of the length of its body). It is the only who pollinates one plant called Centropogon nigricans, despite the existence of other species of bats in the same habitat of the plant. This raises the question of whether evolution is well defined, and occurs between pairs of species or it is diffuse due to the interaction of multiple species.

PREDATOR-PREY RELATIONSHIPS

The cheetah (Acinonyx jubatus) is the fastest vertebrate on land (up to 115 km/h). Thomson’s gazelle (Eudorcas thomsonii), the second (up to 80 km/h). Cheetahs have to be fast enough to catch a gazelle (but not all, at risk of disappearing themselves) and gazelles fast enough to escape almost once and reproduce. The fastest gaelles survive, so nature selects in turn faster cheetahs, which are who eat to survive. The pressure from predators is an important factor that determines the survival of a population and what strategies should follow the population to survive. Also, the predators will find solutions to possible new ways of life of their prey to succeed.

Cheetah hunting a Thomson’s gazelle in Kenya. Photo by Federico Veronesi

The same applies to other predator-prey relationships, parasite-host relationships, plants-herbivores, improving their speed or other survival strategies like poison, spikes…

HUMAN AND DOGS … AND BACTERIA

Our relationship with dogs since prehistoric times, it is also a case of coevolution. This allows, for example, to create bonds with just looking at them. If you want more information, we invite you to read this post where we talk about the issue of the evolution of dogs and humans in depth.

Another example is the relationship we have established with the bacteria in our digestive system, essential for our survival. Or with pathogens: they have co-evolved with our antibiotics, so using them indiscriminately has favored these species of bacteria to develop resistance to antibiotics.

THE IMPORTANCE OF COEVOLUTION

Coevolution is one of the main processes responsible for the great biodiversity of the Earth. According to Thompson, is responsible for the millions of species that exist instead of thousands.

The interactions that have been developed with coevolution are important for the conservation of species. In cases where evolution has been very close between two species, if one become extint will lead to the extinction of the other almost certainly. Humans constantly alter ecosystems and therefore biodiversity and evolution of species. Just declining one species, we are affecting many more. This is the case of the sea otter (Enhydra lutris), which feeds on sea urchins.

Sea otter (Enhydra lutris) eating sea urchins. Photo by Vancouver Aquarium

Being hunted for their fur, urchins increased number, devastated entire populations of algae (consumer of CO2, one of the responsible of global warming), seals who found refuge in the algae nonexistent now were more hunted by killer whales… the sea otter is therefore a key species for the balance of this ecosystem and the planet, as it has evolved along with urchins and algae.

Coevolutive relations between flowers and animals depend on the pollination of thousands of species, including many of agricultural interest, so we must not lose sight of the seriousness of the issue of the disappearance of a large number of bees and other insects in recent years. A complex case of coevolution that directly affects us is the reproduction of fig.

TO SUMMARIZE

As we have seen, coevolution is the evolutionary change through natural selection between two or more species that interact reciprocally.

It is needed:

• Specificity: the evolution of each feature of a species is due  to selective pressures of the feature of the other species.
• Reciprocity: features evolve together.
• Simultaneity: features evolve simultaneously.

REFERENCES

• Massa R (2007). Atlas ilustrado del origen de la vida: La evolución de las especies. Jaca Book spa, Milano.
• Muchhala N. Nectar bat stows huge tongue in its rib cage. Nature (2006) vol. 444 (7120) pp. 701-702
• Coevolución: patrones y procesos
• Celebrando a Darwin
• Los 10 mamíferos más rápidos de la tierra
• La coevolución y las enseñanzas de Darwin
• Coevolución
• Las nutrias marinas pueden salvar nuestro planeta

Symbiosis: relationships between living beings

Predation, parasitism, competition… all living beings, besides interacting with the environment, we relate to other living beings. What types of relationships in addition to those you know? Do you feel like to know them?

INTRODUCTION

The group of all living beings in an ecosystem is called biocenosis or community. The biocenosis is formed in turn by different populations, which would be the set of individuals of the same species occupying an area. For survival, it is imperative that relations between them are established, sometimes beneficial and sometimes harmful.

INTERESPECIFIC RELATIONSHIPS

They are those that occur between individuals of different species. This interaction it is called symbiosis. Symbiotic relationships can be beneficial to a species, both, or harmful to one of the two.

Detrimental to all the species involved:

• Competition: occurs when one or more resources are limiting (food, land, light, soil …). This relationship is very important in evolution, as it allows natural selection acts by promoting the survival and reproduction of the most successful species according to their physiology, behavior …

Rainforests are a clear example of competition between vegetals in the search for light. Kuranda rainforest, Australia. Photo by Mireia Querol

One species has benefits and the other is detrimented:

• Predation: occurs when one species (predator) feeds on another (prey). This is the case of cats, wolves, sharks …

Great white shark (Carcharodon carcharias) jumping to depretade a marine mamal, maybe a sea lion. Photo taken from HQ images.

• Parasitism: one species (parasite) lives at the expense of other (host) and causes it injury. Fleas, ticks, pathogenic bacteria… are the best known, but there are also vertebrate parasites, like the cuckoo that lay their eggs in the nests of other birds, which will raise their chicks (brood parasitism). Especially interesting are the “zombie parasites”, which modify the behavior of the host. Read this post to learn more!

  

  Reed warbler (Acrocephalus scirpaceus) feeding a cuckoo’s chick (Cuculus canorus). Photo by Harald Olsen

  Parasites that live inside the host’s body are called endoparasites (such as tapeworms), and those who live outside ectoparasites (lice). Parasitism is considered a special type of predation, where predator is smaller than prey, although in most cases does not cause the death of the host. When a parasite causes illness or death of the host, it is called pathogen.

  

  Cymothoa exigua is a parasite that replaces the tongue of fish with their own body. Picture by Marcello Di Francesco.

Kleptoparasitism is stealing food that other species has caught, harvested or prepared. This is the case of some raptors, whose name literally means “thief.” See in this video a case of kleptoparasitism on an owl:

Kleptoparasitism can also occur between individuals of the same species.

One species has benefits and the other is not affected:

• Commensalism: one species (commensal) uses the remains of food from another species, which does not benefit or harm. This is the case of bearded vultures. It is also commensalism the use as transportation from one species over another (phoresy), as barnacles attached to the body of whales. The inquilinism is a type of commensalism in which a species lives in or on another. This would apply to the woodpeckers and squirrels that nest in trees or barnacles living above mussels. Finally, metabiosis is the use of the remains of a species for protection (like hermit crabs) or to use them as tools.

  

  The woodpecker finch (Camarhynchus pallidus) uses cactus spines or small branches to remove invertebrates from the trees. Picture by Dusan Brinkhuizen.

  Both species have benefits:

• Mutualism: the two species cooperate or are benefited. This is the case of pollinating insects, which get nectar from the flower and the plant is pollinated. Clownfish and anemones would be another typical example, where clown fish gets protection and food scraps while keeps predators away and clean parasites of the sea anemonae. Mutualism can be optional (a species do not need each other to survive) or forced (the species can not live separately). This is the case of mycorrhizae, an association of fungi and roots of certain plants, lichens (mutualism of fungus and algae), leafcutter ants …

  

  Atta and Acromyrmex ants (leafcutter ants) establish mutualism with a fungus (Leucocoprinus gongylophorus), in which they gather leaves to provide nutrients to the fungus, and they feed on it. It is an obligate mutualism. Photo taken from Ants kalytta.

INTRAESPECIFIC RELATIONSHIPS

They are those that occur between individuals of the same species. They are most beneficial or collaborative:

• Familiars: grouped individuals have some sort of relationship. Some examples of species we have discussed in the blog are elephants, some primates, many birds, cetaceans … In such relationships there are different types of families.
• Gregariousness: groups are usually of many unrelated individuals over a permanent period or seasonal time. The most typical examples would be the flocks of migratory birds, migration of the monarch butterfly, herds of large herbivores like wildebeest, shoal of fish …

  

  Gregariousness of these zebras, along with their fur, allow them to confuse predators. Photo taken from Telegraph

• Colonies: groups of individuals that have been reproduced asexually and share common structures. The best known case is coral, which is sometimes referred to as the world’s largest living being (Australian Great Barrier Reef), but is actually a colony of polyps (and its calcareous skeletons), not single individual.
• Society: they are individuals who live together in an organized and hierarchical manner, where there is a division of tasks and they are usually physically different from each other according to their function in society. Typical examples are social insects such as ants, bees, termites …

Intraspecific relations of competition are:

• Territoriality: confrontation or competition for access to the territory, light, females, food… can cause direct clashes, as in the case of deer, and/or develop other strategies, such as marking odor (cats, bears…), vocalization …

  

  Tiger figthing for territory. Video caption by John Varty

• Cannibalism: predation of one individual over another of the same species.

And you, as a human, have you ever thought how do you relate with individuals of your species and other species?

REFERENCES

• Zompopas
• Relacions de la biocenosi
• Ecología de las comunidades
• Els ecosistemes (xtec)
• National Geographic

The secret life of bees

If we talk about bees, the first thing that comes to mind might be the picture of a well-structured colony of insects flying around a honeycomb made of perfectly constructed wax cells full of honey.

But the truth is that not all bees known nowadays live in hierarchical communities and make honey. Actually, most species of bees develop into a solitary life-form unlike the classical and well-known honey bees (which are so appreciated in beekeeping).

Through this article, I’ll try to sum up the different life-forms of bees in order to shed light on this issue.

INTRODUCTION

Bees are a large diverse group of insects in Hymenoptera order, which also includes wasps and ants. To date, there are up to 20,000 species of bees known worldwide, although there could be more unidentified species. They can be found in most habitats with flowering plants located in every continent of the world (except for the Antarctica).

Bees pick up pollen and nectar from flowers to feed themselves and their larvae. Thanks to this, they contribute on boosting the pollination of plants. Thus, these insects have an enormous ecological interest because they contribute to maintain and even to enhance flowering plant biodiversity on their habitats.

Specimen of Apis mellifera or honey bee (Picture by Leo Oses on Flickr)

However, even though the way they feed and the sources of food they share could be similar, there exist different life-forms among bees which are interesting to focus on.

BEE LIFE-FORMS

SOLITARY BEES (ALSO KNOWN AS “WILD BEES”)

Most species of bees worldwide, contrary to the common knowledge, develop into a solitary life-form: they born and grow alone, they mate once when groups of male and female bees meet each other and, finally, they die alone too. Some solitary bees live in groups, but they never cooperate with each other.

Female of solitary life-form bees build a nest without the help of other bees. Normally, this kind of nest is composed by one or more cells, which are usually separated by partition walls made of different materials (clay, chewed vegetal material, cut leaves…). Then, they provide these cells with pollen and nectar (the perfect food for larvae) and, finally, they lay their eggs inside each cell (normally one per cell). Contrary to hives, these nests are often difficult to find and to identify with naked eyes because of its discreetness.

Solitary bee nest. In this picture we can see the partition walls, pollen and eggs inside each cell (Picture from USDA).

The place where solitary bees build their nest is highly variable: underground, inside twisted leaves, inside empty snail shells or even inside pre-established cavities made by human or left behind by other animals.

These bees don’t make hives nor honey, so these are probably the main reasons because of what they are less popular than honey bees (Apis mellifera). Although solitary bees are the major contributors on pollination due to their abundance and diversity (some of them are even exclusive pollinators of a unique plant species, which reveals a close relation between both organisms), most of the studies related with bees are focused on honey bees, because of what studies and protection of these solitary life-forms still remain in the background.

There exists a large diversity of solitary bees with different morphology:

1) Specimen of Andrena sp. (Picture by kliton hysa on Flickr). 
2) Specimen of Xylocopa violacea or violet carpenter bee (Picture by Nora Caracci fotomie2009 on Flickr).
3) Specimen of Anthidium sp. (Picture by Rosa Gambóias on Flickr).

There are also parasite life-forms among solitary bees, that is, organisms that benefit at the expense of another organism, the host; as a result, the host is damaged in some way. Parasitic bees take advantage of other insects’ resources and even resources from other bees causing them some kind of damage. This is the case of Nomada sp. genus, whose species lay their eggs inside other bee nests (that is, their hosts), so when they hatch, parasite larvae will eat the host’s resources (usually pollen and nectar) leaving them without food. Scientists named this kind of parasitism as cleptoparasitism (literally, parasitism by theft) because parasitic larvae steal food resources from the host larvae.

Specimen of Nomada sp. (Picture by Domingo Roldan on Flickr)

PSEUDOSOCIAL BEES

From now on, we are going to stop talking about solitary bees and begin to introduce the pseudosocial life-forms, that is, bees that live in relatively organized and hierarchical groups which are less complex than truly social life-forms, also known as eusocial life-forms (which is the case of Apis mellifera).

Probably, the most famous example is the bumblebee (Bombus sp.). These bees live in colonies in which the queen or queens (also known as fertilized females) are the ones who survive through the winter. Thus, the rest of the colony dies due to cold. So is thanks to the queen (or queens) that the colony can arise again the next spring.

Specimen of Bombus terrestris or buff-tailed bumblebee(Picture by Le pot-ager "Je suis Charlie" on Flickr).

EUSOCIAL BEES

Finally, the most evolved bees known nowadays in terms of social structure complexity are eusocial bees or truly social bees. Scientist have identified only one case of eusocial bee: the honey bee or Apis mellifera.

Since the objective of this article was to refute the “all bees live in colonies, build hives and make honey” myth, I will not explain further than the fact these organisms form complex and hierarchical societies (this constitutes a strange phenomenon which has also been observed in thermites and ants) normally led by a single queen, build large hives formed of honeycombs made of wax, and make honey, a very energetic substance highly appreciated by humans.

Specimens of Apis mellifera on a honeycomb full of honey (Picture by Nicolas Vereecken on Flickr).

As we have been seeing, solitary bees play an important role in terms of pollination, because of what they must be more protected than they currently are. However, honeybees, and not solitary bees, still remain being on the spotlight of most scientists and a great part of society because of the direct resources they provide to humans.

REFERENCES

• Notes taken during my college practices at CREAF (Centre de Recerca Ecològica i d’Aplicacions Forestals – Ecological Research and Forest Applications Centre). Environmental Biology degree, UAB (Universitat Autònoma de Barcelona).
• O’toole, C. & Raw A. (1999) Bees of the world. Ed Blandford
• Pfiffner L., Müller A. (2014) Wild bees and pollination. Research Institute of Organic Agriculture FiBL (Switzerland).
• Solitary Bees (Hymenoptera). Royal Entomological Society: http://www.royensoc.co.uk/insect_info/what/solitary_bees.htm
• Stevens, A. (2010) Predation, Herbivory, and Parasitism. Nature Education Knowledge 3(10):36

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